Electrical signals are conventionally propagated from one part of a given semiconductor IC chip to another part thereof by means of metal lines on an insulator, the latter in turn typically being in contact with (and supported by) insulator on semiconductor material. Signal propagation on such conventional lines is relatively slow, due at least in part to the relatively high dielectric constant of semiconductor material.
The relatively slow signal propagation speed on conventional transmission lines is becoming a significant problem, at least in very fast (e.g., picosecond) integrated electronic assemblies. For example, a 50 Gbit/sec data rate exemplarily requires a 50 GHz clock signal and its complement, which can be distributed less than 1 mm (using metal lines of GaAs) before timing errors between devices become important.
It is well known that air has a very low dielectric constant, essentially the same as that of vacuum. Thus, the signal propagation speed on a conductor that is configured such that essentially no field lines that originate or terminate on the conductor enter a dielectric other than air would be approximately equal to the speed of light in vacuum, the highest possible signal propagation speed.
A further important aspect of high frequency intra-chip signal transmission is dispersion, especially dispersion associated with the presence of higher order modes. It is known that higher order modes in microstrip lines typically are strongly associated not with the conductive strip but with the dielectric-air interface. See, for instance, Microstrip Lines and Slotlines, K. C. Gupta et al., Artech House, Inc., Washington 1979, p. 65.
Waveguides comprising a conductor strip supported within a conductive housing are known. See, for instance, F. Alessandri et al., IEEE Transactions on Microwave Theory and Techniques, Vol. 37(12), pp. 2020-2027. See also S. Loualiche et al., Electronics Letters, Vol. 26(4), pp. 266-267, wherein is disclosed a non-integrated microwave assembly that comprises an air gap stripline on an InP substrate. However, such waveguides clearly can not be produced by conventional semiconductor manufacturing techniques and can not readily be integrated into a semiconductor IC chip. They thus are not suitable as intrachip conductors.
The prior art also knows so-called airbridges that are typically used to reduce parasitic capacitance between two conductor lines. See, for instance, the paper by J. F. Jensen et al., in Picosecond Electronics and Optoelectronics II, F. J. Leonberger et al., editors, Springer Verlag 1987, pp. 184-187. Such airbridges typically constitute only a minor portion of the total length of a conductor line and clearly introduce an undesirable dielectric constant discontinuity into the transmission path.
In view of the relatively low signal propagation speed associated with prior art intra-chip conductors, it would clearly be very desirable to have available an integrated electronic assembly that comprises intra-chip conductor means that support signal propagation speeds substantially in excess of those associated with conventional prior art conductors, that are substantially free of dielectric discontinuity, and that preferably are of a geometry that is relatively free of field lines that cross an air-dielectric interface, such that generation of higher order modes is relatively low. This application discloses such assemblies.